The Importance of Light
Power of Light - and its use in therapy
Our main natural source of light during the day is the Sun whilst at night our light historically came from campfire, moon and stars. Such light exposure affects humans via two main routes: it enters the brain via the eyes, and superficial parts of the body via the skin. Light absorbed in these two ways affects almost every bodily function, including circadian rhythms and behavior.
For example, the change from night to day at sunrise promotes biological 'clock' effects - waking, increases in steroid secretion, and feeding. Fire light consists of visible, red, infrared and some ultraviolet light. Firelight benefits social function and relaxation. The circadian pattern of light exposure is important for health. But with the advent of electric light, this pattern has changed dramatically in most parts of the world. Gentle night lights have been replaced by artificial electric lights (and screens of electrical devices) to the detriment of our health.3a .14 The resulting disturbance to circadian rhythm have harmful effects on mood, metabolism, immune defence, and cancer risk.7
However, the benefits of daylight can be channeled if used at the right times and in the right ways. Sunlight consists of a spectrum of different light wavelengths or electromagnetic radiation, some of which are not visible to the human eye.
The 'visible' part of the sunlight spectrum are the coloured lights that we see in a rainbow (or when light has been split by a prism); VL can be classified into primarily four categories, according to the wavelength and color: these are blue light, green light, yellow light and red light, with the wavelength of 400–490 nm, 490–570 nm, 570–595 nm, and 630–770 nm, respectively. The longer the wavelength, the deeper the VL can penetrate into the skin. Therefore, red light can penetrate through the full thickness of the epidermis and dermis, reaching the subcutaneous layer, while blue light has less penetration. The sources of VL can be divided into three categories: natural light, artificial light and electronic devices. UV refers to ultraviolet; IR to infrared radiation. Each of these colour wavelength of light has specific effects on humans and on health and disease.46
Ultraviolet light (not visible) is the wavelength most infamously associated with skin tanning and skin damage . But recently it has been shown that visible light can also affect skin pigmentation and ageing - some beneficially, and some not.
The light wavelengths that we are interested in are the near-infrared and the visible (red, orange, yellow green, blue, indigo, violet, and 'white').